This invention relates to an integrated system for converting oxygenates, such as methanol or dimethyl ether (DME), to liquid hydrocarbons. In particular it provides a continuous process for producing liquid hydrocarbon products by converting the oxygenate feedstock catalytically to an intermediate lower olefinic stream for upgrading to produce light distillate and/or gasoline products.
In order to provide an adequate supply of liquid hydrocarbons for use as synfuels or chemical feedstocks, various processes have been developed for converting coal and natural gas to gasoline and distillate. A substantial body of technology has grown to provide oxygenated intermediates, especially methanol. Large scale plants can convert methanol or similar aliphatic oxygenates to liquid fuels, especially gasoline. However, the demand for heavier hydrocarbons has led to the development of processes for making high octane gasoline and quality diesel fuel by a multi-stage technique, utilizing mainly C.sub.3.sup.+ olefins for upgrading.
Recent developments in zeolite catalysts and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks for producing C.sub.5.sup.+ gasoline, diesel fuel, etc. In addition to the basic work derived from ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of new industrial processes.
The medium pore ZSM-5 type catalysts are particularly useful for converting methanol and other lower aliphatic alcohols or corresponding ethers to olefins. Particular interest has been directed to a catalytic process for converting low cost methanol to valuable hydrocarbons rich in ethene and C.sub.3.sup.+ alkenes. Various processes are described in U.S. Pat. Nos. 3,894,107 (Butter et al), 3,928,483 (Chang et al), 4,025,571 (Lago), 4,423,274 (Daviduk et al) and 4,433,189 (Young), incorporated herein by reference. It is generally known that the methanol-to-olefins (MTO) process can be optimized to produce a major fraction of C.sub.2 -C.sub.4 olefins. Prior process proposals have included a separation section to recover ethene and other gases from byproduct water and C.sub.5.sup.+ hydrocarbon liquids.